This invention relates to magnetic memory disks and more specifically, to an improved polishing material for disk substrate polishing.
As the computer industry continues to improve and to increase the magnetic recording densities of the magnetic memory disk, the disk substrate must also evolve. The industry is currently using higher purity aluminum alloys for the substrate to help reduce the number of magnetic defects which are caused by the substrate. When an aluminum substrate has contaminants or alloy materials such as iron, manganese or silicon; the particles of such materials tend to be torn from the surface rather than being sheared off or burnished down during surface finish operations. This causes magnetic imperfections in the resulting magnetic media as small domains of much thicker magnetic coating are randomly present. Small surface irregularities did not significantly impair performance when a fifty millionths thickness magnetic coating was used to form relatively large magnetic domains with track densities of about 500 tracks per inch and bit densities did not exceed 10,000 bits per inch. However with a 10 millionths of an inch magnetic coating thickness, a quarter micron deep void doubles the coating thickness. This becomes even more serious with small magnetic domains as track densities exceed 1000 per inch and bit densities exceed 20,000 per inch. However, the reduction of impurities reduces the hardness of the now almost pure aluminum substrate. This makes such processes as polishing harder to preform.
U.S. Pat. No. 4,393,628 teaches a method and shows a media composition and structure that produces superior results in superfinishing the contemporary magnetic disk substrates. To polish the recently developed substrates of purer alloys, it is necessary to have a polishing material which remains durable and yet will still polish the softer, higher purity aluminum alloys.